Interpretive Summary: Pastures containing multiple forage species have been shown to increase forage productivity compared to pastures planted with a single forage species. While previous work has evaluated whole sward effects on animal productivity, little is known regarding the effects of individual plant species within the sward on diet selection and intake by grazing animals. An essential first step is to improve our understanding of how characteristics of the individual forage species within these mixed swards affect bite mass and intake by grazing animals. Our aim in the present study was to investigate intake characteristics of individual grass species found in mixed-species pastures. Four grass species were grown in micro-sward boxes, then fed to steers in short-term intake tests. The results indicate that the best sward variables for predicting bite mass were tiller length, sward height, and sward mass. While this experiment demonstrated that morphological characteristics affected bite mass of various grass species, much more is yet to be learned about other factors that may affect intake characteristics of forage species found in mixed-species pastures which can lead to management recommendations that result in improved economic and environmental sustainability of pasture-based systems.

Technical Abstract:
Four grass species (Lolium perenne L., Holcus lanatus L. cv Glen, Agrostis stolonifera L. cv Kromi, and Poa trivialis L.) commonly found in mesotropic lowland semi-natural grassland communities in the UK were sown in boxes (85 x 44 x 14 cm) to create micro-swards. Once established, the micro-swards were defoliated at 21-day intervals before being offered to yearling Simmental x Holstein steers in short-term tests. The boxes were weighed (+/- 0.1 g) before and after a 5-min period during which the steers were allowed to take approximately 50 bites. Mean dry matter (DM) bite mass was greatest for L. perenne (0.50 g DM bite-1 vs. mean 0.36 g DM bite-1 for the other treatments). Number of bites taken from the boxes did not differ (mean 32 bites). Extended tiller length (ETL) was greatest for L. perenne (17.32 cm) and least for P. trivialis (13.06 cm). Leaf length was greatest for L. perenne and H. lanatus (mean 6.70 cm) and least for A. stolonifera (4.02 cm). L. perenne had the greatest sward surface height (SSH; 17.10 cm vs. mean 12.98 cm for the other three grass species). Sward DM was lowest for L. perenne (19.70% DM) and highest for A. stolonifera and P. trivialis (mean 23.38 % DM). Regression analyses indicated that the best sward variables for predicting mean DM bite mass were ETL, SSH, and sward DM. While this experiment demonstrated that morphological characteristics affected bite mass of various grass species, much more is yet to be learned about other factors that may affect intake characteristics of species found in semi-natural grasslands which can lead to management recommendations that result in improved economic and environmental sustainability.